1 /* 2 * Copyright (c) 1995 3 * The Regents of the University of California. All rights reserved. 4 * 5 * This code contains ideas from software contributed to Berkeley by 6 * Avadis Tevanian, Jr., Michael Wayne Young, and the Mach Operating 7 * System project at Carnegie-Mellon University. 8 * 9 * %sccs.include.redist.c% 10 * 11 * @(#)lock.h 8.7 (Berkeley) 04/27/95 12 */ 13 14 #ifndef _LOCK_H_ 15 #define _LOCK_H_ 16 17 /* 18 * XXX This belongs in <machine/param.h>, but is here for now. 19 */ 20 #define NCPUS 1 21 22 /* 23 * A simple spin lock. 24 * 25 * This structure only sets one bit of data, but is sized based on the 26 * minimum word size that can be operated on by the hardware test-and-set 27 * instruction. It is only needed for multiprocessors, as uniprocessors 28 * will always run to completion or a sleep. It is an error to hold one 29 * of these locks while a process is sleeping. 30 */ 31 struct simple_lock { 32 int lock_data; 33 }; 34 35 /* 36 * XXX end of stuff that belongs in <machine/param.h> 37 */ 38 39 /* 40 * The general lock structure. Provides for multiple shared locks, 41 * upgrading from shared to exclusive, and sleeping until the lock 42 * can be gained. 43 */ 44 struct lock { 45 struct simple_lock lk_interlock; /* lock on remaining fields */ 46 u_int lk_flags; /* see below */ 47 int lk_sharecount; /* # of accepted shared locks */ 48 int lk_exclusivecount; /* # of recursive exclusive locks */ 49 int lk_waitcount; /* # of processes sleeping for lock */ 50 int lk_prio; /* priority at which to sleep */ 51 char *lk_wmesg; /* resource sleeping (for tsleep) */ 52 int lk_timo; /* maximum sleep time (for tsleep) */ 53 pid_t lk_lockholder; /* pid of exclusive lock holder */ 54 }; 55 /* 56 * Lock request types: 57 * LK_SHARED - get one of many possible shared locks. If a process 58 * holding an exclusive lock requests a shared lock, the exclusive 59 * lock(s) will be downgraded to shared locks. 60 * LK_EXCLUSIVE - stop further shared locks, when they are cleared, 61 * grant a pending upgrade if it exists, then grant an exclusive 62 * lock. Only one exclusive lock may exist at a time, except that 63 * a process holding an exclusive lock may get additional exclusive 64 * locks if it explicitly sets the LK_CANRECURSE flag in the lock 65 * request, or if the LK_CANRECUSE flag was set when the lock was 66 * initialized. 67 * LK_UPGRADE - the process must hold a shared lock that it wants to 68 * have upgraded to an exclusive lock. Other processes may get 69 * exclusive access to the resource between the time that the upgrade 70 * is requested and the time that it is granted. 71 * LK_EXCLUPGRADE - the process must hold a shared lock that it wants to 72 * have upgraded to an exclusive lock. If the request succeeds, no 73 * other processes will have gotten exclusive access to the resource 74 * between the time that the upgrade is requested and the time that 75 * it is granted. However, if another process has already requested 76 * an upgrade, the request will fail (see error returns below). 77 * LK_DOWNGRADE - the process must hold an exclusive lock that it wants 78 * to have downgraded to a shared lock. If the process holds multiple 79 * (recursive) exclusive locks, they will all be downgraded to shared 80 * locks. 81 * LK_RELEASE - release one instance of a lock. 82 * LK_DRAIN - wait for all activity on the lock to end, then mark it 83 * decommissioned. This feature is used before freeing a lock that 84 * is part of a piece of memory that is about to be freed. 85 * 86 * These are flags that are passed to the lockmgr routine. 87 */ 88 #define LK_TYPE_MASK 0x00000007 /* type of lock sought */ 89 #define LK_SHARED 0x00000001 /* shared lock */ 90 #define LK_EXCLUSIVE 0x00000002 /* exclusive lock */ 91 #define LK_UPGRADE 0x00000003 /* shared-to-exclusive upgrade */ 92 #define LK_EXCLUPGRADE 0x00000004 /* first shared-to-exclusive upgrade */ 93 #define LK_DOWNGRADE 0x00000005 /* exclusive-to-shared downgrade */ 94 #define LK_RELEASE 0x00000006 /* release any type of lock */ 95 #define LK_DRAIN 0x00000007 /* wait for all lock activity to end */ 96 /* 97 * External lock flags. 98 * 99 * These flags may be set in lock_init to set their mode permanently, 100 * or passed in as arguments to the lock manager. 101 */ 102 #define LK_EXTFLG_MASK 0x000000f0 /* mask of external flags */ 103 #define LK_NOWAIT 0x00000010 /* do not sleep to await lock */ 104 #define LK_SLEEPFAIL 0x00000020 /* sleep, then return failure */ 105 #define LK_CANRECURSE 0x00000040 /* allow recursive exclusive lock */ 106 /* 107 * Internal lock flags. 108 * 109 * These flags are used internally to the lock manager. 110 */ 111 #define LK_WANT_UPGRADE 0x00000100 /* waiting for share-to-excl upgrade */ 112 #define LK_WANT_EXCL 0x00000200 /* exclusive lock sought */ 113 #define LK_HAVE_EXCL 0x00000400 /* exclusive lock obtained */ 114 #define LK_WAITDRAIN 0x00000800 /* process waiting for lock to drain */ 115 #define LK_DRAINED 0x00001000 /* lock has been decommissioned */ 116 /* 117 * Control flags 118 * 119 * Non-persistent external flags. 120 */ 121 #define LK_INTERLOCK 0x00010000 /* unlock passed simple lock after 122 getting lk_interlock */ 123 #define LK_RETRY 0x00020000 /* vn_lock: retry until locked */ 124 125 /* 126 * Lock return status. 127 * 128 * Successfully obtained locks return 0. Locks will always succeed 129 * unless one of the following is true: 130 * LK_FORCEUPGRADE is requested and some other process has already 131 * requested a lock upgrade (returns EBUSY). 132 * LK_WAIT is set and a sleep would be required (returns EBUSY). 133 * LK_SLEEPFAIL is set and a sleep was done (returns ENOLCK). 134 * PCATCH is set in lock priority and a signal arrives (returns 135 * either EINTR or ERESTART if system calls is to be restarted). 136 * Non-null lock timeout and timeout expires (returns EWOULDBLOCK). 137 * A failed lock attempt always returns a non-zero error value. No lock 138 * is held after an error return (in particular, a failed LK_UPGRADE 139 * or LK_FORCEUPGRADE will have released its shared access lock). 140 */ 141 142 /* 143 * Indicator that no process holds exclusive lock 144 */ 145 #define LK_KERNPROC ((pid_t) -2) 146 #define LK_NOPROC ((pid_t) -1) 147 148 void lock_init __P((struct lock *, int prio, char *wmesg, int timo, 149 int flags)); 150 int lockmgr __P((__volatile struct lock *, u_int flags, 151 struct simple_lock *, pid_t pid)); 152 int lockstatus __P((struct lock *)); 153 154 #if NCPUS > 1 155 /* 156 * The simple-lock routines are the primitives out of which the lock 157 * package is built. The machine-dependent code must implement an 158 * atomic test_and_set operation that indivisibly sets the simple_lock 159 * to non-zero and returns its old value. It also assumes that the 160 * setting of the lock to zero below is indivisible. Simple locks may 161 * only be used for exclusive locks. 162 */ 163 static __inline void 164 simple_lock_init(lkp) 165 struct simple_lock *lkp; 166 { 167 168 lkp->lock_data = 0; 169 } 170 171 static __inline void 172 simple_lock(lkp) 173 __volatile struct simple_lock *lkp; 174 { 175 176 while (test_and_set(&lkp->lock_data)) 177 continue; 178 } 179 180 static __inline int 181 simple_lock_try(lkp) 182 __volatile struct simple_lock *lkp; 183 { 184 185 return (!test_and_set(&lkp->lock_data)) 186 } 187 188 static __inline void 189 simple_unlock(lkp) 190 struct simple_lock *lkp; 191 { 192 193 lkp->lock_data = 0; 194 } 195 196 #else /* NCPUS == 1, so no multiprocessor locking is necessary */ 197 198 #ifdef DEBUG 199 static __inline void 200 simple_lock_init(alp) 201 struct simple_lock *alp; 202 { 203 204 alp->lock_data = 0; 205 } 206 207 static __inline void 208 simple_lock(alp) 209 __volatile struct simple_lock *alp; 210 { 211 extern const char *simple_lock_held; 212 213 if (alp->lock_data == 1) 214 panic(simple_lock_held); 215 alp->lock_data = 1; 216 } 217 218 static __inline int 219 simple_lock_try(alp) 220 __volatile struct simple_lock *alp; 221 { 222 extern const char *simple_lock_held; 223 224 if (alp->lock_data == 1) 225 panic(simple_lock_held); 226 alp->lock_data = 1; 227 return (1); 228 } 229 230 static __inline void 231 simple_unlock(alp) 232 struct simple_lock *alp; 233 { 234 extern const char *simple_lock_not_held; 235 236 if (alp->lock_data == 0) 237 panic(simple_lock_not_held); 238 alp->lock_data = 0; 239 } 240 241 #else /* !DEBUG */ 242 #define simple_lock_init(alp) 243 #define simple_lock(alp) 244 #define simple_lock_try(alp) (1) /* always succeeds */ 245 #define simple_unlock(alp) 246 #endif /* !DIAGNOSTIC */ 247 248 #endif /* NCPUS == 1 */ 249 250 #endif /* !_LOCK_H_ */ 251